No one is going to replace senior developers. But senior developer pay WILL decrease relative to its historical values.
Think wider. You, sharperguy, are not and will not the only person with access to these tools. Therefore, your productivity increase will likely be the same as everyone else's. If you are as good as everyone else, why would YOU get paid more? Have you ever seen a significant number of companies outside FAANG permanently boost everyone's salary just because they they did well on a given year?
A company's goal is to the shareholders not to you. Your value exists relative to that of others.
Not necessarily, there are many factors at play here which are downplayed. The first one is education: LLMs are going to significantly improve skill training. Arguably, it is already happening. So the gap between you and a middev will get narrower. At the same time, candidates who can be as good as you will increase.
While you can argue that you possess specialised skills that not many do, you are unlikely to prove that under pressure within a couple of hours and certainly not to the level where you can have late 10s level of negotiating power imo.
At the end of the day, the market can stay irrational longer than you can continue refuse to accept a lower offer imo. I believe there will be winners. But pure technical skill isn't the moat you think it is. Not anymore.
If every coal miner could suddenly produce 10x the amount of goal, do people say "well now we can just hire one coal miner instead of 10". Or do they say "now thousands of new project which were not economically viable due to the high price of coal are now viable, meaning we actually need to increase our total output beyond even 10x of what it was previously."
Plus, look at the job market. Every single tech company out there has been laying off devs in the last 3 years. If maximising productivity above expenses was so valuable, every tech company out there would be hiring like crazy because senior devs are cheap as chips nowadays. But they aren't, devs might be cheap but money itself isn't right now so they are prioritising lower expenses over increased productivity. Because that makes shareholders happy. And that's what every company aims for.
Maximising productivity is only an absolute goal in the minds of devs not in the minds of executives.